1,3-Propanediol (PDO), as an important raw material for chemical industry, can be used as an organic solvent in inks, dyeing and printing, coatings, lubricants, or antifreezer industry and the like. 1,3-Propanediol mainly acts as a monomer in the synthesis of polyesters and polyurethane, especially to polymerize with terephthalic acid to form polytrimethylene terephthalate (PTT), which exhibits better performances compared to those polymers synthesized from 1,2-propanediol, butanediol and glycol monomer. Now, tens of million tons polyethylene terephthalates (PET) are consumed every year throughout the world. PTT is comparable to PET in chemical stability, biodegradability, and the like, but more excellent in pollution resistance, toughness, elastic resilience, UV resistance and the like. In addition, PTT also has other advantages, such as abrasion resistance or wearability, low water absorption, low static electricity etc., capable of competing with nylon in carpet market. It also can be used in non-woven fabrics, engineering plastics, clothes, domestic decorates, liner materials, fabrics and the like. PTT was evaluated as one of the top six new petrochemicals in USA in 1998, and considered as the update product instead of PET.
The excellent performance and marketing potential of PTT have been recognized 50 years ago. It is very difficult to produce PTT in a large industrial scale just due to the high technical difficulty and cost in the production of its raw material, 1,3-propanediol. So far, only two international corporations, Dupont and Shell, produce self-used 1,3-propanediol for their PTT synthesis from ethylene oxide or propylene as raw materials via a conventional chemical synthesis route. There are several deficiencies in chemical synthesis processes, including excessive by-products; poor selectivity; requiring special operating conditions, such as high temperature and pressure; enormous equipment costs; its raw materials being non-reproducible resources; and ethylene oxide and the intermediate product acrolein produced in another route being combustible, explosive or virulent hazardous matters, respectively. The fermentation process for producing 1,3-propanediol has been focused in recent years due to the high selectivity and the mild operation conditions.
As a by-product in the 1,3-propanediol fermentation, 2,3-butanediol also is an important raw material in chemical industry. It is a colorless and flavorless liquid, and may be used as fuels, and used to prepare polymers, inks, perfumes, antifreezers, fumigants, humidizers, softening agent, plasticizer, explosives, chiral vehicles for pharmaceuticals and the like. Also, 2,3-butanediol may serve as a very valuable raw material in chemical industry to synthesize other chemicals, for example, dehydrating 2,3-butanediol to form methyl ethyl ketone with quite extensive applications, and further dehydrating to form 1,3-butadiene. 2,3-Butanediol can be polymerized to produce styrene via a Diels-Alder reaction. 2,3-Butanediol and methyl ethyl ketone may condense and then subject to a hydrogenating reaction to form octane, which can be used to produce high quality materials for flight. 2,3-Butanediol reacts with acetic acid to form 2,3-butanediol diacetate, which can be added to butters to improve flavor. Generally, 2,3-butanediol, however, is not be separated and purified as a product due to its low yields in the 1,3-propanediol fermentation.
Presently, there are two major methods for producing 1,3-propanediol, chemical and biological methods. Compared to chemical synthesis methods, microbe fermentation methods for producing 1,3-propanediol possess many significant advantages, including mild production conditions, good selectivity, less by-products, easy to separate and purify, without environmental pollution etc., and more and more attention is thereby paid to such methods.
At present, there are several paths for producing 1,3-propanediol by biological methods:
1. Intestinal bacteria are utilized to convert glycerol to 1,3-propanediol under anaerobic conditions (see, U.S. Pat. No. 5,254,467, EP0373230 A1).
2. Anaerobic fermentation with bacteria such as Klebsiella under anaerobic conditions to produce 1,3-propanediol (Ruch et al. Regulation of glycerol catabolism in Klebsiella aerogenes. J Bacteriol. 1974, 119(1):50-56; Streekstra et al. Overflow metabolism during anaeric growth of Klebsiella pneumoniae NCTC418 on glycerol and dihydroxyacetone in chemostat culture. Arch Microbiol. 1987, 147:268-275; Zeng et al. Pathway analysis of glycerol fermentation by Klebsiella pneumoniae: Regulation of reducing equivalent balance and product formation. Enzyme Microbiol Technol. 1993, 15:770-779).
3. Klebsiella are utilized under microaerobic conditions to produce 1,3-propanediol by fermentation (see, Wang Jianfang etc., Study on microaerobic conversion of glycerin to 1,3-propanediol by Klebsiella pneumoniae, Modern Chemical Industry, 2001, 21(5): 28-31; and Chinese Patent Publication No. CN1348007, a method for microaerobic fermentive production of 1,3-propanediol, issued to Xiu Zhilong etc.).
4. Klebsiella are utilized under anaerobic conditions to produce 1,3-propanediol and 2,3-butanediol by fermentation (Biebl et al. Fermentation of glycerol to 1,3-propanediol and 2,3-butanediol. Appl Microbiol Biotechnol, 1998, 50:24-29).
5. 1,3-propanediol and 2,3-butanediol are produced from glycerol by a two-stage microbial fermentation method (Liu Dehua etc., Patent Application No. 200410037692.3).
6. A method for 1,3-propanediol production by a two-step microbial fermentation (Xiu Zhilong etc., Chinese Patent No. ZL01138769.6).
The above methods 1-3 all utilize glycerol as substrates to produce a single product 1,3-propanediol, and the concentration of 1,3-propanediol in broth is very low, so its production costs are very high. Method 4 proposes a fermentation for simultaneously producing 1,3-propanediol and 2,3-butanediol, however, its fermentation level is very low due to the limitations of technical conditions. Method 5 adopts a new process using an anaerobic condition in earlier stage and an aerobic condition in later stage, which significantly increases the concentrations of the fermentation products 1,3-propanediol and 2,3-butanediol, and to some extent, decreases the production costs; but the production costs are still relatively high because this method also utilizes glycerol as substrates. Method 6 provides a two-step fermentation method to produce 1,3-propanediol from raw materials such as starches, which, theoretically, may markedly decrease production costs; but, due to the limitations of technical conditions, the concentration of glycerol is only 49.9 g/L with a yield of only 39.1% by mole, and the 1,3-propanediol concentration is also very low and only 13.18 g/L with a yield of only 22.8% by mole in its most preferred embodiments.